1. Technical Field
The present invention relates to internal communication systems, and more particularly to a system configured to optimize the static slot size of a time-triggered communication protocol with homogeneous slot sizes.
2. Background Art
Internal communication protocols have been developed to support the instrument panels, clusters and otherwise electrical components of transportation machines, such as automobiles, aircrafts, recreational vehicles, and boats. Conventional protocols and in-vehicle networking standards, such as Local Interconnect Networks (LIN), Media Oriented System Transport (MOST), and Controller Area Network (CAN) systems, control electrical communication between various nodes and a host controller, so as to enable inter-nodal function. In automobiles, for example, electro-mechanical power-assisted steering and anti-lock brakes typically utilize a communication network and protocol to receive electric signals from a controller, which communicates with various sensors and actuators. As functionality in transportation machines become increasingly driven by electro-mechanical and electric means, the necessary capacity, flexibility, and reliability of these protocols and network systems become increasingly critical for proper and safe operation. The introduction of advanced control systems that often combine multiple sensors, actuators and electronic control units place boundary demands on conventional communication systems.
As a result, one type of communication system, the FlexRay™ communications protocol (“FlexRay”), has been developed for increasing the bandwidth, determinism, flexibility, scalability, and fault-tolerance of automotive electronic systems. In contrast to conventional event-triggered protocols, FlexRay combines a time-triggered along with an event-triggered system. Generally, the FlexRay protocol presents a multi-channeled communications medium, wherein each channel includes static and dynamic segments during a communication cycle. In the static segment, requirements such as latency and jitter are addressed by deterministic communication timing. A plurality of time-divisible-multiple-access (TDMA) slots of homogenous duration comprises the static segment and re-occurs each cycle. The TDMA slots are manually sized prior to automation, and each slot is accordingly allocated to a node connected to the system, so that the node is able to constantly, and without collision, communicate with the network. The remaining bandwidth includes a dynamic segment divided into a plurality of mini-slots, wherein each mini-slot is configured to receive an event-triggered message of variable size, such as diagnosis data.
Once manually implemented, however, the FlexRay protocol presents a one-size-fits all application that limits bandwidth efficiency. More particularly, during multiple cycles, the static slots transmit varying sets of messages having differing numbers and sizes. For message sets smaller than the ideal set for which the slots were sized, transmission of empty or excessively large slots during a cycle wastes bandwidth, and thereby causes undue delays in the overall system, and reduces the responsiveness of the nodes. For message sets larger than the ideal set for which the slots were sized, the rigidity of the protocol results in excessive time-triggered backlog. Finally, transmission of empty or excessively large slots also reduces available event-triggered bandwidth, which may further result in event-triggered backlog or slow response.
Thus, there is currently a trade-off between having many small slots that incur large protocol overhead and haying a few large slots that cause wasted bandwidth for small messages. To further effect the benefits of the FlexRay protocol, for example, there is a need in the art for an improved time-triggered system that more efficiently determines the optimal static slot size for a given set of messages.